Gas generating composition

ABSTRACT

There is provided a gas generating composition in which the concentration of NOx and so on in the fuel gas is low. The gas generating composition comprises a fuel, a metal hydroxide such as aluminum hydroxide, and a binder, wherein the content of the metal hydroxide in the composition is in the range of 0.5 to 15 mass %, and the content of the binder in the composition is in the range of 1.0 to 4.5 mass %. Because the concentration of NOx and so on in the fuel gas is low, in the case of use in an air bag gas generator, passenger safety upon inflation of the air bag is high.

TECHNICAL FIELD

The present invention relates to a gas generating composition used in an air bag gas generator.

BACKGROUND ART

As gas generating agents used in air bag gas generators, highly safe non-azide-based gas generating compositions comprising any of various nitrogen-containing organic compounds have been developed. There are various requirements on gas generating compositions from the viewpoint of being used in air bag gas generators. As one of these, from the viewpoint of securing passenger safety, the combustion gas is required to be clean, i.e. the amounts of nitrogen oxides (NOx), carbon monoxide, ammonia and so on contained in the combustion gas are required to be as low as possible.

JP-A No. 10-502610 discloses adding glass powder to a fuel such as a tetrazole compound and strontium nitrate, thus lowering the combustion temperature, resulting in a reduction in the amounts of NOx and CO.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a gas generating composition, used in an air bag gas generator, in which the amounts of NOx, carbon monoxide, ammonia and so on contained in the combustion gas upon the gas generating composition being burned are further reduced.

The present inventor discovered that when using a combination of a well known metal hydroxide and binder as components of a gas generating composition, by making the contents thereof be within specific ranges, and further making the ratio between these contents be within a specific range, the amounts of NOx, carbon monoxide, ammonia and so on can be greatly reduced, and hence passenger safety upon air bag inflation can be improved, thus accomplishing the present invention.

As means for solving the problem, the present invention provides a gas generating composition comprising a fuel, a metal hydroxide and a binder, wherein the content of the metal hydroxide in the composition is in the range of 0.5 to 15 mass %, and the content of the binder in the composition is in the range of 1.0 to 4.5 mass %.

By using the gas generating composition of the present invention in an air bag gas generator, the amounts of NOx, carbon monoxide, ammonia and so on contained in the combustion gas produced upon activation of the gas generator can be greatly reduced, and hence passenger safety upon inflation of the air bag by this combustion gas can be improved.

PREFERRED EMBODIMENT OF THE INVENTION

There are no particular limitations on the fuel used in the present invention, with examples being ones used in well known gas generating compositions. As the fuel, at least one selected from tetrazole compounds, guanidine compounds, triazine compounds and nitroamine compounds is preferable.

Examples of tetrazole compounds include 5-aminotetrazole and ammonium bitetrazole; examples of guanidine compounds include guanidine nitrate, mono-, di- and tri-aminoguanidine nitrate, and nitroguanidine; examples of triazine compounds include melamine, cyanuric acid, ammeline, ammelide and ammelande; examples of nitroamine compounds include cyclo-1,3,5-trimethylene-2,4,6-trinitramine.

The content of the fuel in the composition is preferably in the range of 15 to 60 mass %, more preferably 20 to 50 mass %, yet more preferably 25 to 50 mass %.

There are no particular limitations on an oxidizing agent used in the present invention as required, with examples being ones used in well known gas generating compositions. As such an oxidizing agent, at least one selected from nitrates, perchlorates, chloric acid, basic metal nitrates, ammonium nitrate, and so on is preferable.

Examples of nitrates include alkali metal nitrates such as potassium nitrate and sodium nitrate, and alkaline earth metal nitrates such as strontium nitrate; examples of perchlorates include potassium perchlorate, sodium perchlorate, magnesium perchlorate and ammonium perchlorate; examples of basic metal nitrates include basic copper nitrate.

The content of the oxidizing agent in the composition is preferably in the range of 30 to 85 mass %, more preferably 35 to 70 mass %, yet more preferably 40 to 60 mass %.

An example of the metal hydroxide used in the present invention is at least one selected from magnesium hydroxide, aluminum hydroxide, calcium hydroxide, zirconium hydroxide, cobalt hydroxide, and copper hydroxide; of these, magnesium hydroxide, aluminum hydroxide, or a mixture thereof is preferable.

By adjusting the mean particle diameter of the metal hydroxide, the overall dispersibility when mixing with the fuel and so on can be improved; this is preferable, since then the mixing operation becomes easy, and moreover the ignitability of the composition obtained is improved.

The mean particle diameter of the metal hydroxide is preferably in the range of 0.1 to 70 μm, more preferably 0.5 to 50 μm, yet more preferably 2 to 30 μm. The mean particle diameter is that measured by a particle size distribution method using scattered laser light. The measurement sample used is obtained by dispersing the metal hydroxide in water, and then irradiating with ultrasound for 3 minutes; the 50% particle count cumulative value (D₅₀) is determined, and the mean value over two measurements is taken as the mean particle diameter.

To achieve the object of the present invention, the content of the metal hydroxide in the composition is in the range of 0.5 to 15 mass %, preferably 2 to 13 mass %, more preferably 5 to 11 mass %.

There are no particular limitations on the binder used in the present invention, with examples being ones used in well known gas generating compositions. As the binder, at least one selected from carboxymethyl cellulose, sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, ammonium carboxymethyl cellulose, cellulose acetate, cellulose acetate butyrate, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, ethyl hydroxyethyl cellulose, hydroxypropyl cellulose, carboxymethyl ethyl cellulose, microcrystalline cellulose, polyacrylamide, aminated polyacrylamide, polyacrylhydrazide, an acrylamide-metal acrylate copolymer, apolyacrylamide-polyacrylic ester copolymer, polyvinyl alcohol, acrylic rubber, guar gum, starch and silicone is preferable.

To achieve the object of the present invention, the content of the binder in the composition is in the range of 1.0 to 4.5 mass %, preferably 1.5 to 4.0 mass %, more preferably 2.0 to 3.5 mass %.

To achieve the object of the present invention, the mass ratio between the metal hydroxide and the binder (metal hydroxide /binder) is preferably in the range of 15/1 to 1/2, more preferably 10/1 to 1/1, yet more preferably 7/1 to 1/1.

In the present invention, from the viewpoint of lowering the combustion temperature of the gas generating composition, regulating the burning rate, and reducing the amounts of toxic nitrogen oxides and carbon monoxide produced after the combustion, additives can be further included.

Examples of such additives are at least one from metal oxides such as copper oxide, iron oxide, zinc oxide, cobalt oxide, manganese oxide, molybdenum oxide, nickel oxide, bismuth oxide, gallium oxide, silica and alumina, metal carbonates or basic metal carbonates such as cobalt carbonate, calcium carbonate, magnesium carbonate, basic zinc carbonate and basic copper carbonate, composite compounds of a metal oxide or a hydroxide such as Japanese acid clay, kaolin, talc, bentonite, diatomaceous earth and hydrotalcite, metal acid salts such as sodium silicate, mica molybdate, cobalt molybdate and ammonium molybdate, molybdenum disulfide, calcium stearate, silicon nitride and silicon carbide.

The gas generating composition of the present invention can be molded into a desired shape, and thus made into a molded article having the form of a single-perforated cylinder, a porous cylinder, or pellets. Such a molded article can be manufactured using a method in which water or an organic solvent is added to the gas generating composition and mixing is carried out, and then extrusion molding is carried out (for a molded article having the form of a single-perforated cylinder or a porous cylinder), or a method in which compression-molding is carried out using a pelletizer or the like (for a molded article having the form of pellets).

The gas generating composition of the present invention can be used, for example, in any of various vehicles in a driver air bag gas generator, a front passenger air bag gas generator, a side air bag gas generator, an inflatable curtain gas generator, a knee bolster gas generator, an inflatable seat belt gas generator, a tubular system gas generator, or a pretensioner gas generator.

Moreover, a gas generator using the gas generating composition of the present invention may be either a pyrotechnic type in which gas is supplied from the gas generating composition only, or a hybrid type in which gas is supplied from both the gas generating composition and a compressed gas such as argon.

Furthermore, the gas generating composition of the present invention can also be used as an igniting agent called an enhancer (or a booster) for transferring energy from a detonator or a squib to a gas generating agent.

EXAMPLES Examples 1 to 6

A total of 5,000 g of the various components of each composition shown in Table 1 and 737 g of water were put into a mixer and mixing was carried out. The mixture was extruded using an extruder, and cutting and drying were carried out, thus obtaining a gas generating composition in a single-perforated shape having an outside diameter of approximately 4.2 mm, an inside diameter of approximately 1.1 mm, and a length of approximately 4.1 mm. There was no problem with the moldability for any of the compositions. A prescribed amount of each of the gas generating compositions (the mass shown in Table 1) was put into a chamber of inside diameter 57 mm and height 32 mm, and the chamber was sealed, thus forming a test gas generator.

Using each gas generator, a 2800 liter tank exhaust gas test was carried out. In the 2800 liter tank test, the inflator was set in an iron tank having an internal volume of 2800 liters, ignition was carried out, the concentrations of NO, NO₂, CO and NH₃ in the tank after 3 minutes, 15 minutes and 30 minutes were measured using a detector tube, and the mean value of the gas concentrations after 3 minutes, 15 minutes and 30 minutes was taken as the concentration for the gas in question.

The results are shown in Table 1. In Table 1, ‘GN’ is guanidine nitrate, ‘BCN’ is basic copper nitrate, and ‘CMCNa’ is sodium carboxymethyl cellulose. TABLE 1 Gas generating Amount of composition composition (composition; mass %) (g) NO NO₂ CO NH₃ Example 1 GN/BCN/Al(OH)₃/CMCNa 39.4 7.6 0.0 95.8 24.1 (40.71/49.29/5/5) Example 2 GN/BCN/Al(OH)₃/CMCNa 40.8 6.8 0.0 70.0 12.7 (36.98/48.02/10/5) Example 3 GN/BCN/Al(OH)₃/CMCNa 39.2 5.0 0.0 58.3 5.8 (42.78/44.72/10/2.5) Example 4 GN/BCN/Al(OH)₃/CMCNa 38.5 6.0 0.0 66.7 6.7 (45.1/43.4/10/1.5) Example 5 GN/BCN/Al(OH)₃/CMCNa 38.8 5.3 0.0 60.0 7.7 (43.94/44.06/10/2.0) Example 6 GN/BCN/Al(OH)₃/CMCNa 39.5 7.7 0.0 55.0 6.7 (41.62/45.38/10/3.0) The gas concentrations in the table show the proportions in ppm in terms of mass out of the whole gas.

The NO, NO₂, CO and NH₃ concentrations shown in Table 1 are extremely low, and hence it was confirmed that passenger safety upon inflation of an air bag through combustion of the gas generating composition will be high. 

1. A gas generating composition comprising a fuel, a metal hydroxide and a binder, wherein the content of the metal hydroxide in the composition is in the range of 0.5 to 15 mass % and the content of the binder in the composition is in the range of 1.0 to 4.5 mass %.
 2. The gas generating composition as claimed in claim 1, wherein the metal hydroxide is at least one selected from the group consisting of aluminum hydroxide, magnesium hydroxide, calcium hydroxide, zirconium hydroxide, cobalt hydroxide and copper hydroxide.
 3. The gas generating composition as claimed in claim 1, wherein the metal hydroxide is at least one selected from the group consisting of aluminum hydroxide, magnesium hydroxide and a mixture thereof.
 4. The gas generating composition as claimed in claim 1 or 2, wherein the mass ratio between the metal hydroxide to the binder is in the range of 15/1 to 1/2.
 5. The gas generating composition as claimed in claim 1 or 2, wherein the binder is at least one selected from the group consisting of carboxymethyl cellulose, sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, ammonium carboxymethyl cellulose, cellulose acetate, cellulose acetate butyrate, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, ethyl hydroxyethyl cellulose, hydroxypropyl cellulose, carboxymethyl ethyl cellulose, microcrystalline cellulose, polyacrylamide, aminated polyacrylamide, polyacrylhydrazide, an acrylamide-metal acrylate copolymer, a polyacrylamide-polyacrylic ester copolymer, polyvinyl alcohol, acrylic rubber, guar gum, starch and silicone.
 6. The gas generating composition as claimed in claim 1 or 2, further comprising an oxidizing agent. 